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SELECT 
  1 
FROM 
  cscart_lock_keys 
WHERE 
  key_id = 'c21b3bdc21687c81a05e629a593c200d35e7a5872f2e23705148288270c4c3a2' 
  AND token = '3KAw12/evUGnbWmc40iEGw0aXncySNi2uUuQqRfFm/4=' 
  AND expiry_at > UNIX_TIMESTAMP(NOW())

Query time 0.00025

JSON explain

{
  "query_block": {
    "select_id": 1,
    "message": "no matching row in const table"
  }
}